In German Published Patent Application No. 197 06 682 is discussed a method of anisotropic high-rate plasma etching of silicon with SiO2, formed from the addition of SiF4 and O2 to the actual SF6 etching agent, being used as a side wall passivating material. At the same time, CHF3, CF4, C2F6, or C4F8 are added to the etching gas continuously or at determined intervals as SiO2-consuming additives (“scavengers”) in order to selectively strip the SiO2 on the structure base.
Another high-rate etching method for silicon is discussed, for example, in German Patent No. 42 41 045, where a high-density plasma source using inductive high-frequency excitation (ICP source) or a special microwave excitation (PIE source) is used for releasing fluorine radicals from a fluorine-delivering etching gas and for releasing (CF2)x radicals from a passivating gas that delivers teflon-forming monomers, to form a teflon-type passivating material, with etching gas and passivating gas being used alternately.
In German Published Patent Application No. 43 17 623, it is known that a mixture of SF6 or another fluorine-delivering etching gas and CHF3 or another passivating gas forming teflon-type monomers can be exposed to a high-density plasma, so that the fluorine radicals etch the silicon structure base and at the same time the teflon-type monomers form a passivating material on the structure side walls thus ensuring an anisotropic character of the etching process.